Vehicle alarm system

ABSTRACT

A sensitive current detector includes the vehicle ammeter and is responsive to current therein to activate a first pulser which sets a monostable multivibrator which activates another pulser having an output to the vehicle horn relay to sound the horn at a 2-cycle per second (Hz.) frequency. The monostable multivibrator resets after 1 minute of sounding of the horn to deactivate the horn unless the current detector continues to sense current. A delay timer responds to a key-operated switch or a remote disable switch to inhibit, for 15 seconds, activation of the sound pulser by the monostable. The monostable multivibrator can also be set by mechanically operable switches.

United States Patent 3,533,064 10/1970 Perelman ABSTRACT: A sensitive current detector includes the vehicle ammeter and is responsive to current therein to activate a first pulser which sets a monostable multivibrator which activates another pulser having an output to the vehicle horn relay to sound the horn at a -cycle per second (l-lz.) frequency. The monostable multivibrator resets after 1 minute of sounding of the horn to deactivate the horn unless the current detector continues to sense current. A delay timer responds to a keyoperated switch or a remote disable switch to inhibit, for 15 seconds, activation of the sound pulser by the monostable. The monostable multivibrator can also be set by mechanically operable switches.

VEHICLE ALARM SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to alarm systems, and more particularly to a comparatively simple and inexpensive, but reliable system which is responsive, with high sensitivity, to electric current usage in a vehicle electrical system.

. 2. Description of the Prior Art Alarm systems of considerable variety are known in the art. Yet there remains to be solved the specific problems created by new and different environments for alarms, new technology, and the ever present demand for lower cost and improved performance.

Vehicle alarm systems are known which respond to mechanical stimuli such as the opening of a window, or a door, or a hood. Another is known which uses an inductive coupling to a battery cable to initiate an alarm. Yet these devices have aspects which are considered disadvantageous in certain respects. It is an object of the present invention to provide a system meeting requirements as outlined above and providing a combination of features advantageous over systems currently known.

SUMMARY or THE INVENTION Described briefly, in a typical embodiment of the present invention, solid-state circuitry is employed throughout and includes a two-transistor constant current source whose output is varied in response to small current usage in the vehicle electrical system, as by the illumination of a courtesy lamp upon opening a door, for example. The change in output is effective, after a predetermined initial delay, to set a multivibrator to initiate an alarm pulser, the pulser remaining activated to pulse the vehicle horn during the period of the monostable multivibrator prior to automatic reset thereof. A key switch is employed through appropriate time delay means to activate and deactivate the alarm system. A remote disabling switch and associated delay circuitry facilitates short term disablement of the system when desired by the proprietor thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a typical embodiment of the present invention.

FIG. 2 is a schematic diagram thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, and particularly the block diagram of FIG. 1, the current detector 11 is coupled to the ammeter 12 of the vehicle and responsive to current therein, after the keylock-operated switch 13 is closed, to activate the pulser 14 which, in turn, activates the alarm switch 16. The steady state output of the alarm switch, once set by the pulser l4, activates the alarm pulser l7 producing a pulse output to the vehicle horn relay coil 18, to pulse the vehicle horn 19.

A delay timer 21 connected to the alarm switch 16 is activated initially upon activation of the alarm system by closing the key switch 13 to permit closing of doors or trunk lids or other activity by the proprietor of the system (owner of the car, for example) for a predetermined period of the order of seconds, for example. The delay timer may also be activated by closure of a disable switch 22 at any time after the alarm system has been activated by the key switch. Such a disable switch can be a magnetically operated reed switch located at some secret location on the vehicle. This permits temporary (15 second) disablement of the system by the proprietor to permit this entry into the vehicle, for example. Such a reed switch could be operated by temporarily holding a magnet near the switch as, for example, adjacent a corner of the windshield. In either event, the delay timer disables the alarm switch 16 from activating the alarm pulser for a period of approximately 15 seconds.

A mechanical switch 23 is provided and connected to some vehicle component such as a hood 24, for example, operation of this switch being effective to activate the alarm switch 16.

Referring now particularly to Figure 2, the B+ terminal of the vehicle battery is connected to the supply line 26, and return line 27 is connectable to battery ground 28 through the key-operated switch 13. A variety of suitable key-operated locks can be employed for manually opening or closing this switch. The horn relay 18 is shown with one side thereof connected to 3+ and the other side thereof connected through the normally open manually operable horn ring switch 29, the other side of which is at ground 28. One side of the vehicle ammeter is connected to 3+ through line 26, the other side being connectable to ground 28 through any one of a variety of vehicle equipment items designated generally as 32. These can be courtesy lights as indicated above, a radio, ignition primary circuit, or parking light, for example.

As indicated above, the alarm system is activated or armed by closing the keylock'operated switch 13. Although there is an initial delay thereupon initiated, prior to the time when the horn can be sounded by the alarm system, that feature will be described hereinafter. For the present, the various blocks appearing in the block diagram and described generally above, will now be described in more detail.

The current-sensing circuit 11 includes a two-transistor constant current source with the automobile ammeter 12 or suitable current shunt as a part of the current-determining elements. The base-emitter voltage of the diode-connected transistor 0,, (V,,,;,) is determined by the current thru 0,. This voltage appears across the base-emitter junction of Q and across the emitter resistor, R of Q and the ammeter. The base-emitter voltage of Q (V is determined by the current thru 0,. If the current thru 0 is less than the current thru 0,, then V will be less than V This voltage difference is predictable and is about 60 millivolts per decade of current difference. The voltage across the emitter resistor and the ammeter is V ,V,,,, and the current thru 0, is

Veer eer WEsiliA. W

when R A is the meter or shunt resistance.

When current flows thru the ammeter from the battery, (eg. a light is on), the voltage drop across the ammeter will increase. The current, I, will decrease, since The decrease of current, I will cause a corresponding decrease in voltage at the collector of Q and will forward bias switching transistor 0 Resistor R, is a variable resistor for adjustment purposes, and resistor R 2 may be on the order of l ohm for appropriate sensitivity. Diodes CR, and CR are employed for temperature compensation for the switching transistor 0,.

Transistor Q, is normally off when there is no current flow through the ammeter 12. It will turn on when the battery current increases to about I00 milliamperes. When transistor 0;, is turned on, it turns on the gating transistor 0, which begins charging capacitor C, through resistor R,,. The unijunction transistor 0 will be fired when capacitor C, is charged, and will thereupon produce a pulse output at 33. Therefore, in this combination we have an astable multivibrator in the form of a unijunction sawtooth generator. The frequency is about 0.5 pulses per second. The charging time of capacitor C, is established at approximately 2 seconds in order that it be long enough to permit electric winding of .the vehicle clock without firing the unijunction transistor.

The monostable multivibrator 16 includes transistors Q, and Q, and transistors Q, and Q The timing thereof is determined by capacitor C, and resistor R so that when the mul tivibrator is set, it will remain in the set condition for approximately 1 minute and it is during this l-minute period that the alarm is sounding, as will soon be described. Then it will automatically reset.

In its first normal stable state, the multivibrator 16 has transistors and Q, conducting. However, upon application of a pulse through capacitor C from the pulser 14 to the base of transistor 0 to set the multivibrator, the base of O is driven below ground, turning off these transistors and producing a positive going output signal at 34. In addition to the vehicle ammeter current-responsive pulser means of setting the monostable multivibrator, it can be set by closure of the normally open mechanically operated switch 23, grounding the bane of transistor 0,, and turning off this one and thereby transistor 0 to produce the signal output at 34. Closure of the switch 23 could be effected by the opening of the vehicle hood, a door, a window, the luggage compartment, or some other mechanical activity.

When the multivibrator output signal appears on the output line 34, unless it is inhibited from activating the alarm by means of the circuitry 21, it is applied to the base of gating transistor 0,, to fire the second unijunction astable multivibrator 0 which produces a 2-l-lz. pulse to the base of transistor 0, which, through resistor R connected to the base of power transistor Q drives the latter. The power transistor Q grounds the one side of the vehicle horn relay to sound the horn. The frequency of the astable multivibrator using the unijunction Q, establishes the frequency at which the horn is sounded, giving the beeping or pulsating sound. This astable multivibrator will run until the monostable multivibrator 16 automatically resets itself, the timing of which is determined by the resistor R and capacitor C The Z-Hz. frequency of the alarm pulses is determined by capacitor C and resistors R and R it was mentioned above that the monostable multivibrator will automatically reset in approximately 1 minute, thus terminating the beeping" of the vehicle horn. However, if current continues to flow in the vehicle ammeter, it will continue to be sensed by the sensor of the present invention, thus causing the pulser 14 to continue to supply the sharp pulses to the base of transistor Q Consequently the monostable will be triggered again each time it resets, so long as battery current continues to flow through the ammeter 12. Similarly, so long as the mechanical switch 23 remains closed, the monostable multivibrator will not reset or, if it does reset, will immediately be restarted and thereby continue to produce the needed output to the gating transistor 0, to keep the alarm pulser running;

If the keylock operated switch 13 is located inside the vehicle, it is desirable to provide a certain period of delay between the time it is closed to arm the alarm system, and the time the system becomes armed. For this purpose, the initial delay circuitry 21 is provided. Transistor Q is connected between the monostable multioutput 34 and ground. When transistor O is on it will hold Q in saturation, thus inhibiting operation of the alarm pulser by the monostable multi l6.

Q is biased on when transistor 0, is of and will turn on. When the key switch is turned on, (i.e. closed) 0,, is turned on and Q, is off. Capacitor C starts charging thru resistor R As soon as Zener diode CR is forward biased (about 6 V), Q turns on, turning of Q and thereby Q and the monostable multivibrator 16 will no longer be inhibited from operating the alarm pulser.

Where the key-operated switch is located inside the vehicle, it is desirable to provide some means for the operator to disarm the alarm system while he gains access to the interior of the vehicle to open the key switch. One example of means useful for this purpose is the provision of a magnetic reedoperated switch near one of the windows, such as the windshield for example. This switch can be operated by holding a magnet near it and such a switch can be employed as the remote disable switch 22 of the circuitry. Closure of this switch momentarily will discharge capacitor C whereupon the threshold required by. the Zener diode CR for keeping transistor 0,, on will be removed. Thus transistor Q, will turnoff and transistors Q, and thereby Q will again be turned on, and inhibit operation of the alarm-pulser gate Q by the monostable multivibrator 16.

When the remote disable switch reopens after its momentary closure, capacitor C, will again start charging and, when the threshold of the Zener diode is reached, transistor Or: will turn on to remove the inhibiting of the monostable multivibrator operation. ln either event of utilization of the circuitry 21, the inhibit time is about l5 seconds. In normal usage, after the operator of the vehicle disables the alarm system with the remote disable switch, and enters the vehicle, he will utilize the key switch to disable the system. Diode CR permits capacitor C, to discharge immediately when the key switch is turned off to disarm the system.

From the foregoing description, it will be recognized that the present invention has a variety of beneficial features. These include sensing electric current drawn from the battery to sound the alarm, turn-on delay, automatic reset, remote disabling, a pulsating alarm, mechanical switch activation as desired, and alarm delay. The sensor can be adjusted to be immune to steady state currents through the ammeter up to a certain level, if desired, and respond to any currents exceeding that level.

The invention claimed is:

1. In a vehicle having an electrical system, an alarm system comprising:

a current sensor coupled to said electrical system and responsive to a current change therein to produce an output signal;

a first pulser having an input coupled to said sensor and responsive to said signal to produce output pulses;

first switching means coupled to said first pulser and responsive to a pulse therefrom to produce an output signal for a first predetermined period of time;

a second pulser having an input coupled to said first switching means and responsive to said output signal therefrom to produce output pulses; and

alarm means coupled to said second pulser and activated thereby.

2. The alarm system of claim 1 wherein:

said current sensor is responsive to steady state current levels different from a predetermined level to produce said output signal.

3. The alarm system of claim 1 wherein:

said first pulser includes a first delay means to avoid said pulse output thereof in response to said current sensor output signal unless said sensor output signal persists longer than a second predetermined period of time.

4. The alarm system of claim 1 wherein:

said current sensor includes a signal-translating device in se ries with a portion of said vehicle electrical system.

5. The alarm system of claim 1 wherein:

said alarm means include the vehicle horn.

6. The alarm system of claim 1 and further comprising:

second switching means coupled to said first switching means and operable, when actuated, to produce a signal input to said first switching means for activation thereof independent of said sensor means, said switching means being connected to a mechanically operable vehicle component for activating said alarm means in response to movement of said component.

7. The alarm system of claim 1 and further comprising:

delay means coupled to the output of said first switching means and inhibiting the output of a signal from said first switching means to said second pulser for a predetermined delay period.

8. The alarm system of claim 7 wherein:

said delay means include a key-operated switch for arming and disarming the alarm system, and a remotely operable switch for temporary disablernent of the alarm system.

9. The alarm system of claim 1 wherein:

said first pulser is an astable multivibrator;

said first switching means is a monostable multivibrator;

said second pulser is a second astable multivibrator.

10. The alarm system of claim 1 wherein:

said sensor includes a constant current source having a' diode-connected biasing transistor with the emitter-collector path thereof in series with a first impedance means across an energy supply, and a current source transistor having its base coupled to the collector of said biasing transistor and biased thereby, and having its emitter-collector path coupled in series with a second impedance means and a portion of said vehicle electrical system and to said energy supply,

the said current source transistor having an output conductor coupled thereto to produce said output signal thereon.

11. The alarm system of claim wherein:

said vehicle electrical system portion is one in common circuit relationship with a plurality of electrical devices of the vehicle electrical system.

12. The alarm system of claim 11 wherein:

said first pulser includes an electrically operable switch having a control electrode coupled to said output conductor, and switchable by said output signal of said sensor.

13. The alarm system of claim 12 wherein:

said sensor includes in the series coupling of the emitter-collector path of said current source transistor and said second impedance means and said electrical system portion, third impedance means to establish the level of said sensor signal output in response to current flowing in said electrical system portion.

14. The alarm system of claim 13 wherein:

said electrical system portion is the vehicle ammeter. 

1. In a vehicle having an electrical system, an alarm system comprising: a current sensor coupled to said electrical system and responsive to a current change therein to produce an output signal; a first pulser having an input coupled to said sensor and responsive to said signal to produce output pulses; first switching means coupled to said first pulser and responsive to a pulse therefrom to produce an output signal for a first predetermined period of time; a second pulser having an input coupled to said first switching means and responsive to said output signal therefrom to produce output pulses; and alarm means coupled to said second pulser anD activated thereby.
 2. The alarm system of claim 1 wherein: said current sensor is responsive to steady state current levels different from a predetermined level to produce said output signal.
 3. The alarm system of claim 1 wherein: said first pulser includes a first delay means to avoid said pulse output thereof in response to said current sensor output signal unless said sensor output signal persists longer than a second predetermined period of time.
 4. The alarm system of claim 1 wherein: said current sensor includes a signal-translating device in series with a portion of said vehicle electrical system.
 5. The alarm system of claim 1 wherein: said alarm means include the vehicle horn.
 6. The alarm system of claim 1 and further comprising: second switching means coupled to said first switching means and operable, when actuated, to produce a signal input to said first switching means for activation thereof independent of said sensor means, said switching means being connected to a mechanically operable vehicle component for activating said alarm means in response to movement of said component.
 7. The alarm system of claim 1 and further comprising: delay means coupled to the output of said first switching means and inhibiting the output of a signal from said first switching means to said second pulser for a predetermined delay period.
 8. The alarm system of claim 7 wherein: said delay means include a key-operated switch for arming and disarming the alarm system, and a remotely operable switch for temporary disablement of the alarm system.
 9. The alarm system of claim 1 wherein: said first pulser is an astable multivibrator; said first switching means is a monostable multivibrator; said second pulser is a second astable multivibrator.
 10. The alarm system of claim 1 wherein: said sensor includes a constant current source having a diode-connected biasing transistor with the emitter-collector path thereof in series with a first impedance means across an energy supply, and a current source transistor having its base coupled to the collector of said biasing transistor and biased thereby, and having its emitter-collector path coupled in series with a second impedance means and a portion of said vehicle electrical system and to said energy supply, the said current source transistor having an output conductor coupled thereto to produce said output signal thereon.
 11. The alarm system of claim 10 wherein: said vehicle electrical system portion is one in common circuit relationship with a plurality of electrical devices of the vehicle electrical system.
 12. The alarm system of claim 11 wherein: said first pulser includes an electrically operable switch having a control electrode coupled to said output conductor, and switchable by said output signal of said sensor.
 13. The alarm system of claim 12 wherein: said sensor includes in the series coupling of the emitter-collector path of said current source transistor and said second impedance means and said electrical system portion, third impedance means to establish the level of said sensor signal output in response to current flowing in said electrical system portion.
 14. The alarm system of claim 13 wherein: said electrical system portion is the vehicle ammeter. 